Essentially, the main difference, at the risk of getting slightly technical, is that fair dealing in Canada is an exception to infringement. It is a defence that one raises in response to a claim that you have engaged in an act of infringement, so the way that is managed is very different.
In this instance, Bill C-76 was introducing positive obligations—not only that you had to introduce an ads registry, but about the way it had to be done—that we simply couldn't accommodate in the time frame allowed. That's the main difference in the two.